I have grown arum in a pool. Usually fine over winter. However, I always removed it from the pool......wet and cold fatal to so many plants.....so, not knowing where you are (if you are in a cold area) I would keep out of the pool until spring. What have you got to lose by doing this? You could lose if by keeping it in the water. Also when introducing to the water I would place the arum as ??ou have done now and then when growth is vigorous lower it so top of pot is about level with the water surface